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In the uplink, while macrocell mobile stations (mMSs) are synchronized to the macrocell base station (mBS), their signals will arrive asynchronously at the femtocell base station (fBS). For OFDMA, if the timing misalignment among the mMSs is greater than the cyclic prefix duration, intersymbol interference (ISI) and intercarrier interference (ICI) will occur in the received signal at the femtocell...
In this paper, we propose a novel equalization method for OFDM systems without guard interval (GI). The performance of GI-free OFDM system is usually limited by inter-symbol interference (ISI) and inter-carrier interference (ICI). The proposed method is to firstly detect the tail part of transmitted OFDM symbol, then eliminate the ISI and ICI to recover the whole symbol. We find that the tail part...
Multi-carrier modulation and especially CP-OFDM is widely used nowadays in several radio communications. However, FBMC is a potential alternative to CP-OFDM since it does not require cyclic prefix, and thus, it has a higher spectral efficiency. One of the characteristics of FBMC is that the received data are accompanied by a two dimensional inter-symbol interference term (2D ISI), which complicates...
We consider a cellular network MIMO OFDM system where cooperating base stations apply joint signal processing to the receive signals of several users. In this situation, due to geometry, the problem of unavoidable differences in time of arrival between the users' signals occurs. As a result, symbol timing offsets can be larger than the cyclic prefix, which leads to OFDM inter-symbol interference....
For mitigating inter-symbol interference (ISI) and inter-carrier interference (ICI) caused by insufficient cyclic prefix (CP), per-tone equalizer (PTEQ) outperforms traditional time domain equalizer (TEQ) since each tone is equalized independently. However, PTEQ with equal number of taps (equal length) for all the tones can not achieve the optimal performance because channel conditions of different...
This paper investigates the impact of carrier frequency offset (CFO) on Single Carrier wireless communication systems with Frequency Domain Equalization (SC-FDE). We show that CFO in SC-FDE systems causes irrecoverable channel estimation error, which leads to inter-symbol-interference (ISI). The impact of CFO on SC-FDE and OFDM is compared in the presence of CFO and channel estimation errors. Closed...
It is well known that symbol timing offsets larger than the cyclic prefix as well as carrier frequency offsets between transmitter and receiver stations destroy the orthogonality among OFDM subcarriers and induce additional interference. In conjunction with MIMO transmission on frequency selective fading channels where different users interfere with each other, these effects strongly degrades the...
In this paper we present a new adaptive fractional frequency reuse scheme (AFFR) for multi-cell OFDMA based IEEE 802.16e network. The adaptive fractional frequency reuse (AFFR) scheme is managed by the access service network gateway (ASN-GW) which coordinate a set of BSs (one cluster). To make better usage of radio resources; we assume that the cell area is virtually divided into two different zones:...
In this paper, we consider the frequency reuse issue in the downlink of a multi-cell OFDMA system. We first implement the static frequency reuse scheme in the OFDMA sub-carrier assignment over the multi-cell system in order to control the inter-cell interference. Then, we add the random access sub-band to adopt the dynamic frequency reuse. The main purpose of introducing the random access sub-band...
The carrier frequency offset (CFO) could destroy the orthogonality of OFDM subcarriers and induce the inter-carrier interference (ICI) spread. However, the generalized multi-carrier (GMC) system reflects different interference characters in the presence of CFO. In this paper, we exactly analyze the CFO effect on GMC, which multiplexes several single band single carrier based frequency division multiple...
This work analyzes combined effects of major synchronization errors, including the symbol time offset (STO), carrier frequency offset (CFO) and sampling clock frequency offset (SCFO) of orthogonal frequency-division multiplexing (OFDM) systems. Such errors degrade the performance of an OFDM receiver by introducing inter-carrier interference (ICI) and inter-symbol interference (ISI) into the systems...
OFDM/DMT has been proposed as a suitable modulation for power-line communications (PLC). Meanwhile, another modulation, named OFDM/OQAM, was presented to be also an alternative to OFDM. Further, the HS-OQAM system was proposed particularly for the baseband communications such as PLC. This paper gives a theoretical expression of the inter-symbol interference (ISI) plus inter-carrier interference (ICI)...
An orthogonal frequency division multiplexing (OFDM) system suffers performance degradation when the length of the cyclic prefix (CP) is less than the channel impulse response. The root cause of this degradation is the inter-carrier interference (ICI) and inter-symbol interference (ISI) introduced by the excessive multipath delay. Generally, MIMO beamforming is helpful in mitigating such interference...
In this paper we are introducing a new generation of 802.11n wireless network standard. The objective is to obtain numerical values for various measures of networking performance of 802.11n by simulating the system using Simulink. Our initial approach was to investigate the abilities of 802.11n standard to model a transmitter and receiver that communicated over a user defined channel. In wireless...
OFDM systems are known to outperform single-carrier systems in a multipath environment. However, multipath waves, whose delay times are longer than the guard interval, cause intersymbol interference, because of which the performance of the system degrades. The effectiveness of adaptive arrays in overcoming this problem has been investigated. This paper proposes the use of an adaptive array with orthogonal...
In this paper, we investigate cooperative OFDM communications using amplify-and-forward (AF) protocol at the relays, in the presence of imperfect timing synchronization. In most studies on cooperative communications, perfect time synchronization among cooperating nodes is assumed. In practice, however, due to imperfect time synchronization, orthogonality among the subcarriers of the different nodes'...
Orthogonal frequency division multiplexing offset quadrature amplitude modulation (OFDM/OQAM) is a multi carrier modulation using staggered transmission on the I and Q axes. It uses as well an optimized non-rectangular pulse shaping. There are several advantages with respect to the conventional OFDM modulation, while the main drawback is the intrinsic intersymbol interference, hindering e.g. a proper...
In this paper we consider the coexistence issue between OFDM-based WLANs of the 802.11a family and time-hopping ultra wideband (TH-UWB) systems. A general analytical expression is provided for the bit error rate (BER) of the OFDM transceiver operating in the presence of UWB interference and the interferences caused by the multipath propagation phenomenon on the 802.11a OFDM signal, comprising intersymbol...
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